1. Field of the Invention
The invention relates to aeronautics. More particularly, the invention relates to aircraft structure and load accommodation. The invention also relates to cargo loading or discharging, particularly releasable, externally mounted cargo.
2. Discussion of the Related Art
Suspension slings are used for suspending a cargo load below an aircraft during flight. Loads are typically attached to a helicopter with a sling suspension attached to structurally strengthened hard points on the under surface of the fuselage. There is substantial benefit when jettisoning load for suspension from a single cable. Dropping or jettisoning cargo is inherently more balanced because it is accomplished by opening a single attachment hook. However, a single cable system produces an undistributed point load on the aircraft resulting in instability problems. At speeds greater than low speeds, a load will twist on a single cable to a position broadside to the direction of flight. Flight with the widest area facing the direction of flight induces yawing of the load. As a result, the pilot must limit aircraft speed to approximately 50 knots to reduce instability in the aircraft.
In order to overcome the single cable load yawing, loads have been suspended from two or more cables. It has been found that this reduces aerodynamically induced load yawing at lower speeds but yawing resumes at higher speeds. Two or more suspension cables are used for low speed flight but produce instability at higher speeds of 120 knots or more. Aircraft turns may initiate instability at any aircraft speed, especially at higher speeds.
In order to use the capability speed of aircraft, there a need for an attachment apparatus that provides stable suspension of externally mounted cargo loads at higher air speeds.